Environmental Impact Assessment: "Pseudoreplication" in Time?

TLDR

Hurlbert’s monograph highlights problems in sampling design for assessing biological population impacts from effluent discharge, emphasizing the need to target the underlying mean abundance rather than observed counts. The study proposes a sampling scheme to detect effluent discharge effects on the underlying mean abundance. The design uses a BACI approach, sampling before and after discharge at control and impact sites, ensuring control sites are distant yet comparable, and addresses assumptions such as additivity and independence. The design satisfies Hurlbert's criteria in many cases but is unsuitable when control and impact sites have differing long‑term trends, though such situations can be statistically identified.

Abstract

A recent monograph by Hurlbert raised several problems concerning the appropriate design of sampling programs to assess the impact upon the abundance of biological populations of, for example, the discharge of effluents into an aquatic ecosystem at a single point. Key to the resolution of these issues is the correct identification of the statistical parameter of interest, which is the mean of the underlying probabilistic "process" that produces the abundance, rather than the actual abundance itself. We describe an appropriate sampling scheme designed to detect the effect of the discharge upon this underlying mean. Although not guaranteed to be universally applicable, the design should meet Hurlbert's objections in many cases. Detection of the effect of the discharge is achieved by testing whether the difference between abundances at a control site and an impact site changes once the discharge begins. This requires taking samples, replicated in time, Before the discharge begins and After it has begun, at both the Control and Impact sites (hence this is called a BACI design). Care needs to be taken in choosing a control site so that it is sufficiently far from the discharge to be largely beyond its influence, yet close enough that it is influenced by the same range of natural phenomena (e.g., weather) that result in long—term changes in the biological populations. The design is not appropriate where local events cause populations at Control and Impact sites to have different long—term trends in abundance; however, these situations can be detected statistically. We discuss the assumptions of BACI, particularly additivity (and transformations to achieve it) and independence.